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In the title compound, C15H17NO2, the ethoxy­carbonyl group is anti with respect to the pyrrole N atom. The angle between the planes of the phenyl and pyrrole rings is 48.26 (9)°. The mol­ecules are joined into dimeric units by a strong hydrogen bonds between pyrrole N-H groups and carbonyl O atoms. The geometry of the isolated mol­ecule was studied by ab initio quantum mechanical calculations, employing both molecular orbital Hartree-Fock (MO-HF) and density functional theory (DFT) methods. The minimum energy was achieved for a conformation where the angle between the planes of the phenyl and pyrrole rings is larger, and that between the ethoxy­carbonyl and pyrrole planes is smaller than in the solid-state mol­ecule.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102020656/ln1155sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102020656/ln1155Isup2.hkl
Contains datablock I

CCDC reference: 201280

Comment top

The class of pyrroles includes a large number of important compounds (Chadwick, 1990), usually divided into naturally occurring pyrroles with important biological functions (Battersby & McDonald, 1976), and artificial pyrroles used in the pharmaceutical industry and in the medical (Bonnet, 1995) and materials sciences (Grieve et al., 1994; Smith et al., 1996; Richardson et al., 1998). Following our studies on porphyrin synthesis (Sobral & Rocha Gonsalves, 2001), we have been working on the synthesis and structure determination of several substituted pyrroles (Paixão et al., 2002; Ramos Silva et al., 2000; 2002a,b,c), which are intended for incorporation at the β-pyrrole positions of porphyrins. The title compound, (I), was recently synthesized and an X-ray diffraction study was undertaken to clarify the conformation of the molecule, and the results are presented here. \sch

The endocyclic angles of the pyrrole ring of (I) add up to exactly 540°, indicating that the heterocyclic ring is almost perfectly planar. In fact, no atom in the ring deviates by more than 0.005 (1) Å from the least-squares plane. There is a significant asymmetry between the two Nsp2 bonds [N1—C5 1.347 (2) and N1—C2 1.377 (2) Å]. In addition, the C—C bond opposite to the heteroatom is longer than the others. The asymmetry of the C—N bonds can be explained by the electron-withdrawing character of the ethoxycarbonyl group, and by the preferential conjugation of the C6O1 bond with C2 C3, which leads to a stronger interaction between C4C5 and the N1 lone pair, resulting in a shortening of the N1—C5 bond. These effects are reproduced in ab initio quantum mechanical calculations (see below).

The angle between the planes of the phenyl and pyrrole rings is 48.26 (9)°, which contrasts with the value observed in a similar compound, ethyl 4-acetyl-5-methyl-3-phenyl-1H-pyrrole-2-carboxylate monohydrate [76.93 (5)°; Ramos Silva et al., 2002c]. This difference probably occurs because the adjacent methyl substituents in (I) are less sterically hindering than the acetyl and ethoxycarbonyl groups that are adjacent to the phenyl ring in the latter compound.

The ethoxycarbonyl group in (I) adopts an anti conformation with respect to the N atom of the heterocyclic ring (Fig. 1). This group is slightly tilted with respect to the pyrrole ring, the C3—C2—C6—O2 torsion angle being -4.8 (3)°, and is fairly planar, as seen by the C6—O2—C7—C8 torsion angle of 177.7 (2)°. In this group, the large atomic displacement parameter of atom C8, the short C7—C8 bond, and a nearby peak of residual density (0.57 e Å-3) suggest that the terminal methyl group is disordered. However, attempts to model the disorder were unsuccessful.

A strong hydrogen bond between the pyrrole N—H and the carbonyl O atoms links the molecules of (I) into dimeric units (Fig. 2), in a way which is similar to that found in a related compound, benzyl 5-carboxy-4-ethyl-3-methyl-pyrrole-2-carboxylate (Ramos Silva et al., 2000). These interactions form rings with a graph-set motif of R22(10) (Bernstein et al., 1995).

To investigate the effect of the intermolecular interactions on the conformation of the molecule of (I), we have performed an optimization of the geometry of the isolated molecule by ab initio quantum mechanical calculations using the computer program GAMESS (Schmidt et al., 1993), and employing both molecular orbital Hartree-Fock (MO—HF) and density functional theory (DFT) methods. For the latter, a B3LYP functional was chosen and a grid integration method used. In both cases, a standard 6–31 G(d,p) basis set was employed. The optimization was conducted starting from the experimental crystal structure geometry without imposing any symmetry constraints on the molecule. Each self-consistent field calculation was iterated until a Δρ of less than 10-5 bohr-3 was achieved. The final equilibrium geometry at the minimum energy had a maximum gradient in internal coordinates of 10-5 Hartree bohr-1 or Hartree rad-1.

Both HF and DFT calculations closely reproduce the solid-state geometry of the molecule. The C3—C4—C10—C15 torsion angle is calculated to be 60.6 and 50.9° for HF and DFT, respectively, which is slightly larger than the observed value [45.9 (3)°]. The most stable conformation of the ethoxycarbonyl group is anti and coplanar with the pyrrole ring [C3—C2—C6—O2 - 1.0° (HF) or 0.2° (DFT)]. The internal distortions of the heterocyclic ring are well reproduced by the calculations. As usually found, the calculated DFT bond lengths are slightly longer than the HF ones. The HF values are closer to the experimental values at room temperature, but after correction of the crystal structure model for librational motion, the DFT values become closer. The overall discrepancy is less than 0.011 Å between the zero-motion DFT and the corrected experimental data. The calculated DFT distances for N1—C5 and N1—C2 are 1.357 and 1.380 Å, respectively, compared with the librationally corrected experimental values [1.350 and 1.383 Å, respectively]. The DFT and experimental values for the pyrrole ring internal angles differ by less than 0.4°.

Experimental top

The title compound was prepared through a Knorr-type reaction (Paine, 1978) in a 70% yield. Small single crystals of (I) were grown from a solution in dichloromethane-ethanol (1:1) (m.p. 418–419 K). Spectroscopic analysis: IR (ν, cm-1): 1651 (CO), 3302 (N—H); 1H NMR (CDCl3, 200 MHz, δ, p.p.m.): 1.3 (t, CH3—CH2–), 2.2 (s, CH3–), 2.3 (s, CH3–), 4.2 (q, CH3—CH2–), 7.1 (m, –C6H5), 8.8 (m,-NH–). Elemental analysis, calculated for C15H17NO2: C 74.05, H 7.04, N 5.76%; found: C 73.66, H 6.93, N 5.83%.

Refinement top

The methyl H atoms were constrained to an ideal geometry (C—H = 0.96 Å) with Uiso(H) = 1.5Ueq(C), but were allowed to rotate freely about the C—C bonds. The positional and atomic displacement parameters of the H atom bonded to the pyrrole N atom were refined freely. All remaining H atoms were placed in geometrically idealized positions (C—H = 0.93–0.97 Å) and constrained to ride on their parent atoms with Uiso(H) = 1.2Ueq(C). Examination of the crystal structure with PLATON (Spek, 2002) showed that there are no solvent-accessible voids in the crystal lattice.

Computing details top

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: HELENA (Spek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. A view of the molecule of (I), with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
[Figure 2] Fig. 2. A view down the b axis of the unit cell of (I), with the hydrogen bonds shown as dashed lines.
Ethyl 3,5-dimethyl-4-phenyl-1H-pyrrole-2-carboxylate top
Crystal data top
C15H17NO2F(000) = 520
Mr = 243.30Dx = 1.180 Mg m3
Monoclinic, P21/cCu Kα radiation, λ = 1.5418 Å
Hall symbol: -P 2ybcCell parameters from 25 reflections
a = 11.3160 (13) Åθ = 13.3–25.6°
b = 6.744 (2) ŵ = 0.63 mm1
c = 18.4091 (15) ÅT = 293 K
β = 102.887 (8)°Block, colourless
V = 1369.5 (5) Å30.25 × 0.20 × 0.15 mm
Z = 4
Data collection top
Enraf-Nonius MACH3
diffractometer
2215 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.018
Graphite monochromatorθmax = 72.3°, θmin = 4.0°
ω/2θ scansh = 1313
Absorption correction: ψ scan
(North et al., 1968)
k = 07
Tmin = 0.751, Tmax = 0.911l = 2222
5053 measured reflections3 standard reflections every 180 min
2606 independent reflections intensity decay: 4%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.054Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.169H atoms treated by a mixture of independent and constrained refinement
S = 1.07 w = 1/[σ2(Fo2) + (0.0953P)2 + 0.3261P]
where P = (Fo2 + 2Fc2)/3
2606 reflections(Δ/σ)max < 0.001
170 parametersΔρmax = 0.57 e Å3
0 restraintsΔρmin = 0.31 e Å3
Crystal data top
C15H17NO2V = 1369.5 (5) Å3
Mr = 243.30Z = 4
Monoclinic, P21/cCu Kα radiation
a = 11.3160 (13) ŵ = 0.63 mm1
b = 6.744 (2) ÅT = 293 K
c = 18.4091 (15) Å0.25 × 0.20 × 0.15 mm
β = 102.887 (8)°
Data collection top
Enraf-Nonius MACH3
diffractometer
2215 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.018
Tmin = 0.751, Tmax = 0.9113 standard reflections every 180 min
5053 measured reflections intensity decay: 4%
2606 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0540 restraints
wR(F2) = 0.169H atoms treated by a mixture of independent and constrained refinement
S = 1.07Δρmax = 0.57 e Å3
2606 reflectionsΔρmin = 0.31 e Å3
170 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.08411 (13)0.7753 (2)0.01941 (7)0.0628 (4)
N10.07943 (13)1.0948 (2)0.11493 (8)0.0480 (4)
H10.026 (2)1.109 (4)0.0729 (14)0.074 (7)*
O20.24911 (13)0.6564 (2)0.09765 (7)0.0655 (4)
C20.16045 (14)0.9405 (3)0.13282 (9)0.0459 (4)
C60.15884 (16)0.7862 (3)0.07809 (9)0.0487 (4)
C30.23092 (14)0.9768 (3)0.20347 (9)0.0466 (4)
C40.19098 (14)1.1596 (3)0.22732 (9)0.0450 (4)
C50.09618 (14)1.2275 (3)0.17099 (9)0.0467 (4)
C100.24644 (15)1.2691 (3)0.29571 (9)0.0476 (4)
C90.3244 (2)0.8422 (3)0.24883 (11)0.0649 (6)
H9A0.30810.70790.23230.097*
H9B0.32150.85220.30040.097*
H9C0.40340.88020.24280.097*
C160.02067 (19)1.4105 (3)0.16556 (12)0.0627 (5)
H16A0.00301.45140.11440.094*
H16B0.06681.51420.19450.094*
H16C0.05041.38360.18430.094*
C110.17869 (18)1.3577 (3)0.34084 (11)0.0628 (5)
H110.09501.34090.33010.075*
C150.37183 (16)1.2952 (3)0.31516 (11)0.0587 (5)
H150.41981.23570.28640.070*
C140.42634 (19)1.4074 (4)0.37624 (12)0.0684 (6)
H140.51011.42320.38800.082*
C130.3578 (2)1.4948 (4)0.41925 (12)0.0742 (7)
H130.39441.57040.46040.089*
C120.2339 (2)1.4706 (4)0.40152 (12)0.0762 (7)
H120.18681.53090.43070.091*
C70.2565 (2)0.4987 (4)0.04539 (13)0.0735 (6)
H7A0.26290.55370.00230.088*
H7B0.18460.41610.03770.088*
C80.3634 (3)0.3826 (5)0.0771 (2)0.1202 (12)
H8A0.43380.46620.08480.180*
H8B0.37170.27730.04350.180*
H8C0.35550.32760.12380.180*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0769 (9)0.0572 (9)0.0473 (7)0.0071 (7)0.0008 (6)0.0019 (6)
N10.0463 (7)0.0484 (9)0.0462 (7)0.0024 (6)0.0033 (6)0.0008 (6)
O20.0672 (8)0.0633 (9)0.0607 (8)0.0186 (7)0.0032 (6)0.0149 (6)
C20.0453 (8)0.0457 (10)0.0462 (8)0.0032 (7)0.0088 (6)0.0021 (7)
C60.0523 (9)0.0458 (10)0.0474 (9)0.0014 (7)0.0097 (7)0.0037 (7)
C30.0437 (8)0.0486 (10)0.0470 (8)0.0029 (7)0.0092 (7)0.0024 (7)
C40.0413 (8)0.0483 (10)0.0451 (8)0.0000 (7)0.0092 (6)0.0002 (7)
C50.0424 (8)0.0463 (10)0.0502 (9)0.0010 (7)0.0075 (7)0.0001 (7)
C100.0475 (9)0.0471 (10)0.0467 (9)0.0004 (7)0.0076 (7)0.0008 (7)
C90.0669 (12)0.0657 (13)0.0559 (10)0.0198 (10)0.0006 (9)0.0026 (9)
C160.0600 (11)0.0551 (12)0.0678 (11)0.0131 (9)0.0034 (9)0.0034 (9)
C110.0525 (10)0.0774 (14)0.0584 (10)0.0029 (9)0.0124 (8)0.0117 (10)
C150.0476 (9)0.0678 (13)0.0579 (10)0.0002 (8)0.0061 (8)0.0043 (9)
C140.0540 (11)0.0789 (15)0.0637 (11)0.0027 (10)0.0055 (9)0.0062 (11)
C130.0802 (14)0.0731 (15)0.0571 (11)0.0057 (12)0.0106 (10)0.0142 (10)
C120.0728 (13)0.0924 (18)0.0606 (11)0.0126 (12)0.0092 (10)0.0232 (12)
C70.0858 (14)0.0633 (14)0.0695 (13)0.0145 (11)0.0136 (11)0.0175 (10)
C80.126 (3)0.103 (2)0.123 (2)0.047 (2)0.010 (2)0.031 (2)
Geometric parameters (Å, º) top
O1—C61.216 (2)C16—H16A0.9600
N1—C51.347 (2)C16—H16B0.9600
N1—C21.377 (2)C16—H16C0.9600
N1—H10.88 (3)C11—C121.380 (3)
O2—C61.332 (2)C11—H110.9300
O2—C71.449 (2)C15—C141.382 (3)
C2—C31.387 (2)C15—H150.9300
C2—C61.446 (2)C14—C131.360 (3)
C3—C41.416 (3)C14—H140.9300
C3—C91.498 (2)C13—C121.377 (3)
C4—C51.393 (2)C13—H130.9300
C4—C101.474 (2)C12—H120.9300
C5—C161.491 (3)C7—C81.450 (4)
C10—C111.385 (3)C7—H7A0.9700
C10—C151.395 (2)C7—H7B0.9700
C9—H9A0.9600C8—H8A0.9600
C9—H9B0.9600C8—H8B0.9600
C9—H9C0.9600C8—H8C0.9600
C5—N1—C2110.27 (14)C5—C16—H16C109.5
C5—N1—H1123.5 (17)H16A—C16—H16C109.5
C2—N1—H1126.2 (17)H16B—C16—H16C109.5
C6—O2—C7117.20 (15)C12—C11—C10120.81 (19)
N1—C2—C3107.67 (15)C12—C11—H11119.6
N1—C2—C6118.22 (15)C10—C11—H11119.6
C3—C2—C6134.08 (16)C14—C15—C10121.47 (19)
O1—C6—O2122.66 (17)C14—C15—H15119.3
O1—C6—C2124.09 (16)C10—C15—H15119.3
O2—C6—C2113.24 (14)C13—C14—C15120.13 (19)
C2—C3—C4106.73 (15)C13—C14—H14119.9
C2—C3—C9127.02 (17)C15—C14—H14119.9
C4—C3—C9126.08 (16)C14—C13—C12119.6 (2)
C5—C4—C3107.56 (15)C14—C13—H13120.2
C5—C4—C10125.57 (16)C12—C13—H13120.2
C3—C4—C10126.62 (15)C13—C12—C11120.7 (2)
N1—C5—C4107.76 (15)C13—C12—H12119.7
N1—C5—C16121.19 (15)C11—C12—H12119.7
C4—C5—C16131.05 (17)O2—C7—C8107.2 (2)
C11—C10—C15117.31 (17)O2—C7—H7A110.3
C11—C10—C4122.77 (16)C8—C7—H7A110.3
C15—C10—C4119.84 (16)O2—C7—H7B110.3
C3—C9—H9A109.5C8—C7—H7B110.3
C3—C9—H9B109.5H7A—C7—H7B108.5
H9A—C9—H9B109.5C7—C8—H8A109.5
C3—C9—H9C109.5C7—C8—H8B109.5
H9A—C9—H9C109.5H8A—C8—H8B109.5
H9B—C9—H9C109.5C7—C8—H8C109.5
C5—C16—H16A109.5H8A—C8—H8C109.5
C5—C16—H16B109.5H8B—C8—H8C109.5
H16A—C16—H16B109.5
C5—N1—C2—C30.40 (19)C3—C4—C5—N10.67 (19)
C5—N1—C2—C6177.95 (15)C10—C4—C5—N1173.91 (15)
C7—O2—C6—O10.5 (3)C3—C4—C5—C16179.82 (19)
C7—O2—C6—C2178.64 (17)C10—C4—C5—C165.2 (3)
N1—C2—C6—O16.1 (3)C5—C4—C10—C1149.1 (3)
C3—C2—C6—O1176.09 (19)C3—C4—C10—C11137.3 (2)
N1—C2—C6—O2173.02 (15)C5—C4—C10—C15127.6 (2)
C3—C2—C6—O24.8 (3)C3—C4—C10—C1545.9 (3)
N1—C2—C3—C40.80 (19)C15—C10—C11—C121.4 (3)
C6—C2—C3—C4177.18 (18)C4—C10—C11—C12175.4 (2)
N1—C2—C3—C9174.65 (18)C11—C10—C15—C141.0 (3)
C6—C2—C3—C97.4 (3)C4—C10—C15—C14175.90 (19)
C2—C3—C4—C50.91 (19)C10—C15—C14—C130.3 (4)
C9—C3—C4—C5174.60 (18)C15—C14—C13—C120.0 (4)
C2—C3—C4—C10173.60 (16)C14—C13—C12—C110.4 (4)
C9—C3—C4—C1010.9 (3)C10—C11—C12—C131.1 (4)
C2—N1—C5—C40.18 (19)C6—O2—C7—C8177.7 (2)
C2—N1—C5—C16179.43 (16)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O1i0.88 (3)2.02 (3)2.875 (2)164 (2)
Symmetry code: (i) x, y+2, z.

Experimental details

Crystal data
Chemical formulaC15H17NO2
Mr243.30
Crystal system, space groupMonoclinic, P21/c
Temperature (K)293
a, b, c (Å)11.3160 (13), 6.744 (2), 18.4091 (15)
β (°) 102.887 (8)
V3)1369.5 (5)
Z4
Radiation typeCu Kα
µ (mm1)0.63
Crystal size (mm)0.25 × 0.20 × 0.15
Data collection
DiffractometerEnraf-Nonius MACH3
diffractometer
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.751, 0.911
No. of measured, independent and
observed [I > 2σ(I)] reflections
5053, 2606, 2215
Rint0.018
(sin θ/λ)max1)0.618
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.054, 0.169, 1.07
No. of reflections2606
No. of parameters170
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.57, 0.31

Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, HELENA (Spek, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEPII (Johnson, 1976), SHELXL97.

Selected geometric parameters (Å, º) top
O1—C61.216 (2)C3—C41.416 (3)
O2—C61.332 (2)C4—C51.393 (2)
C2—C31.387 (2)C7—C81.450 (4)
C5—N1—C2110.27 (14)C5—C4—C3107.56 (15)
N1—C2—C3107.67 (15)N1—C5—C4107.76 (15)
C2—C3—C4106.73 (15)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O1i0.88 (3)2.02 (3)2.875 (2)164 (2)
Symmetry code: (i) x, y+2, z.
 

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